Piezoelectric pump

ABSTRACT

Embodiments of the present disclosure may include a piezoelectric pump having: a piezoelectric vibrator including a main shim that may be formed of a conductive thin metal plate and a piezoelectric element layer that may be formed on the main shim; and a pair of ring-shaped support members that may support front and rear sides of a circumferential portion of the piezoelectric vibrator such that a pump chamber and an air chamber formed on the front and rear sides of the piezoelectric vibrator may be fluid-tightly sealed. The ring-shaped support members may support both sides of a circumferential portion of the piezoelectric element layer of the piezoelectric vibrator, and the piezoelectric vibrator may be vibrated to perform a pumping operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of the Japanese Patent Application No. 2007-035878 filed on Feb. 16, 2007, the entire content of which is hereby incorporated by reference.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates to a piezoelectric pump that performs a pumping operation using vibrations of a piezoelectric vibrator.

2. Description of the Related Art

For example, JP-A-6-117377 and Japanese Utility Model Registration No. 2510590 disclose piezoelectric pumps including: a piezoelectric vibrator whose periphery is fluid-tightly sealed; a pump chamber and an air chamber that are provided on the front and rear sides of the piezoelectric vibrator; and a pair of check valves (including a check value that allows the flow of liquid to the pump chamber and a check valve that allows the flow of liquid from the pump chamber) that are provided on a pair of flow passages communicating with the pump chamber and allow liquid to flow in opposite directions. When the piezoelectric vibrator is vibrated, the volume of the pump chamber varies, which causes one of the pair of check valves to be opened and the other check value to be closed. This operation is repeated to perform a pumping operation. Such a piezoelectric pump has been used as, for example, a coolant circulating pump for a water-cooled notebook computer.

JP-A-2001-238291 discloses a unimorph type piezoelectric vibrator in which a piezoelectric element is laminated on one surface of a shim formed of a conductive thin metal plate. JP-A-6-203351 discloses a bimorph type piezoelectric vibrator in which piezoelectric elements are provided on both sides of the shim. Regardless of the type of piezoelectric vibrators, in the related art, a pair of ring-shaped sealing members (ring-shaped support members) come into contact with only the front and rear surfaces of the shim, and the piezoelectric element is arranged inside the ring-shaped sealing members, in order to fluid-tightly seal the piezoelectric vibrator. In this case, when the piezoelectric element being deformed (extended or contracted) is pressed, the piezoelectric element is not sufficiently deformed, which results in a reduction in the discharge amount of liquid and an instable pumping operation.

However, the following factors as well as the flow rate of liquid should be considered in the piezoelectric vibrator: high closing pressure (the internal pressure of a discharge passage (system) when intake and discharge umbrellas are closed (when no liquid flows)); and a high mechanical strength of the piezoelectric vibrator. That is, even when the internal pressure is at a high level, it is necessary to prevent the deformation of a piezoelectric vibrator and increase the closing pressure.

SUMMARY

Embodiments of the present disclosure may provide a piezoelectric pump capable of improving the mechanical strength and support strength of a piezoelectric vibrator and increasing the closing pressure thereof while reducing the thickness of a shim.

According to an embodiment of the present disclosure, a piezoelectric pump may include: a piezoelectric vibrator including a main shim that is formed of a conductive thin metal plate and a piezoelectric element layer that is formed on the main shim; and a pair of ring-shaped support members that support front and rear sides of a circumferential portion of the piezoelectric vibrator such that a pump chamber and an air chamber formed on the front and rear sides of the piezoelectric vibrator are fluid-tightly sealed. The ring-shaped support members may support both sides of a circumferential portion of the piezoelectric element layer of the piezoelectric vibrator, and the piezoelectric vibrator may be vibrated to perform a pumping operation.

The piezoelectric vibrator may include one or more shims that are formed of an elastic metal material in a unimorph type or a bimorph type.

In the piezoelectric pump according to an embodiment of the present disclosure, in the piezoelectric vibrator, one surface of the main shim may abut on the pump chamber, and at least one piezoelectric element layer may be formed on the other surface of the main shim. In this example, one of the pair of ring-shaped support members close to the pump chamber may come into contact with a circumferential portion of the main shim, and the other ring-shaped support member close to the air chamber may come into contact with the circumferential portion of the piezoelectric element layer.

In the piezoelectric pump according to an embodiment of the present disclosure, the piezoelectric element layer of the piezoelectric vibrator may include: a lower piezoelectric element layer that is formed on the other surface of the main shim; and an upper piezoelectric element layer that is formed on the lower piezoelectric element layer so as to be electrically insulated from the lower piezoelectric element layer.

In the piezoelectric pump according to an embodiment of the present disclosure, in addition to the main shim, an intermediate shim formed of an elastic metal material having mechanical recovery may be interposed between a plurality of piezoelectric element layers of the piezoelectric vibrator. For example, the intermediate shim may have higher mechanical recovery than the main shim. When the intermediate shim has high mechanical recovery, the intermediate shim may easily be deformed with the displacement of a plurality of piezoelectric element layers, and may rarely hinder the deformation of the plurality of piezoelectric element layers.

In the piezoelectric pump according to an embodiment of the present disclosure, the intermediate shim may have a larger diameter than the piezoelectric element layer formed on the intermediate shim, and the pair of ring-shaped support members may support both sides of a circumferential portion of a laminate of the intermediate shim, the main shim, and the piezoelectric element layer interposed between the two shims. When the piezoelectric element layer of the piezoelectric vibrator is formed in, for example, a two-layer structure of the lower piezoelectric element layer and the upper piezoelectric element layer, the intermediate shim may have a larger diameter than the upper piezoelectric element layer, and may extend to a circumferential portion of the lower piezoelectric element layer. The support members may support both sides of a circumferential portion of the lower piezoelectric element layer with the intermediate shim interposed therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an expanded perspective view illustrating the basic structure of a piezoelectric pump according to an embodiment of the present disclosure;

FIG. 2 depicts a cross-sectional view illustrating the piezoelectric pump according to an embodiment of the present disclosure;

FIG. 3 depicts a partially enlarged cross-sectional view illustrating a support structure of a piezoelectric vibrator according to an embodiment of the present disclosure;

FIG. 4 depicts a cross-sectional view schematically illustrating a support structure according to an embodiment of the present disclosure;

FIG. 5 depicts an expanded perspective view illustrating a support structure of a piezoelectric vibrator according to an embodiment of the present disclosure;

FIG. 6 depicts a cross-sectional view schematically illustrating a support structure according to an embodiment of the present disclosure;

FIG. 7 depicts a cross-sectional view illustrating a support structure of a piezoelectric vibrator according to an embodiment of the present disclosure;

FIG. 8 depicts a cross-sectional view illustrating a support structure of a piezoelectric vibrator according to an embodiment of the present disclosure;

FIG. 9 depicts a cross-sectional view illustrating a support structure of a piezoelectric vibrator according to an embodiment of the present disclosure;

FIG. 10 depicts a cross-sectional view illustrating a S support structure of a piezoelectric vibrator according to an embodiment of the present disclosure;

FIG. 11 depicts an exemplary graph illustrating the relationship between the flow rate and the pressure of liquid flowing through a piezoelectric pump in Example 1 in which a pair of ring-shaped support members support front and rear sides of a circumferential portion of a laminated piezoelectric element and in Comparative example 1 in which a pair of ring-shaped support members support front and rear sides of a circumferential portion of a main shim, according to an embodiment of the present disclosure;

FIG. 12 depicts an exemplary graph illustrating the relationship between the flow rate and the pressure of liquid flowing through a piezoelectric pump in Example 2 in which a pair of ring-shaped support members support front and rear sides of a circumferential portion of a lower piezoelectric element layer of a laminated piezoelectric element and in Comparative example 1 in which a pair of ring-shaped support members support the front and rear sides of the circumferential portion of the main shim, according to an embodiment of the present disclosure; and

FIG. 13 depicts a cross-sectional view schematically illustrating the support structure according to Comparative example 1 shown in FIGS. 11 and 12, according to an embodiment of the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

The disclosure may be designed to support both sides of a circumferential portion of a piezoelectric element with ring-shaped support members while sacrificing the deformation of a piezoelectric vibrator, thereby improving the mechanical strength of the piezoelectric vibrator and thus increasing the closing pressure thereof, unlike the related art in which the ring-shaped support members do not support both sides of the piezoelectric element.

FIGS. 1 and 2 depict a basic structure of a piezoelectric pump according to an embodiment of the present disclosure. A piezoelectric pump 20 may include a lower housing 21, a middle housing 22, and an upper housing 23 laminated from the bottom of FIGS. 1 and 2 in this order.

The lower housing 21 may be provided with an inlet port 24 and a discharge port 25 for a coolant (liquid). A piezoelectric vibrator 10 and a ring-shaped electrode terminal 29 may be fluid-tightly sealed and supported by a pair of ring-shaped support members (an O-ring 27 and a guide 28) between the middle housing 22 and the upper housing 23, and a pump chamber P may be formed between the piezoelectric vibrator 10 and the middle housing 22. An air chamber A may be formed between the piezoelectric vibrator 10 and the upper housing 23. The air chamber A may be opened or airtightly sealed.

An intake passage 30 through which the inlet port 24 and the pump chamber P communicate with each other, and a discharge passage 31 through which the pump chamber P and the discharge port 25 communicate with each other may be formed in the lower housing 21 and the middle housing 22. Check valves (umbrellas) 32 and 33 may be provided in the intake passage 30 and the discharge passage 31 of the middle housing 22, respectively. The check valve 32 may be a suction check value that allows the flow of liquid from the inlet port 24 to the pump chamber P, but prevents the flow of liquid in the opposite direction thereof. The check valve 33 may be a discharge check value that allows the flow of liquid from the pump chamber P to the discharge port 25, but prevents the flow of liquid in the opposite direction thereof. The check valves 32 and 33 according to the embodiment shown in FIGS. 1 and 2 may have the same structure, and may include substrates 32 a and 33 a having openings formed therein that may be adhered to or fixed to the passages by fusing, and umbrellas 32 b and 33 b that may be formed of an elastic material and mounted to the substrates 32 a and 33 a, respectively.

A rectangular concave portion 21 a may be formed in the lower housing 21 at a position isolated from the intake passage 30 and the discharge passage 31, and a driver circuit board 26 for controlling the driving of the piezoelectric vibrator 10 may be fluid-tightly sealed and may be provided between the concave portion 21 a and the middle housing 22.

In the piezoelectric pump 20, when the piezoelectric vibrator 10 is elastically deformed (vibrated) forward and backward, the suction check valve 32 is opened, and the discharge check value 33 is closed during a process of increasing the volume of the pump chamber P, a liquid may flow from the inlet port 24 to the pump chamber P. Meanwhile, during a process of decreasing the volume of the pump chamber P, the discharge check valve 33 may be opened, and the suction check valve 32 may be closed. As a result, a liquid may flow from the pump chamber P to the discharge port 25. Therefore, a pumping operation by elastically deforming (vibrating) the piezoelectric vibrator 10 forward and backward continuously may be performed.

In the piezoelectric pump 20, as described above, the piezoelectric vibrator 10 (and the ring-shaped electrode terminal 29) may be fluid-tightly sealed and supported by a pair of ring-shaped support members (the O-ring 27 and the guide 28) between the middle housing 22 and the upper housing 23. This embodiment may be characterized in the support structure. Next, the piezoelectric vibrator 10 and the support structure thereof will be described in detail with reference to FIGS. 3 to 10.

FIGS. 3 and 4 depict a piezoelectric vibrator 10 and a support structure thereof, according to an embodiment of the present disclosure. FIG. 3 depicts an expanded cross-sectional view illustrating a support structure of the piezoelectric vibrator 10, and FIG. 4 depicts a cross-sectional view schematically illustrating the piezoelectric vibrator 10 and a pair of ring-shaped support members (the O-ring 27 and the guide 28).

The piezoelectric vibrator 10 may include a circular main shim 11 and a circular laminated piezoelectric element 12 formed on one of the front and rear surfaces of the main shim 11.

The main shim 11 may be a conductive thin metal plate with a thickness of about 30 to about 300 μm that is formed of, for example, stainless steel or 42 alloy, and may have sufficient rigidity to support the laminated piezoelectric element 12. The main shim 11 may have a wiring protrusion 11 a for electrical connection in a circumferential portion thereof, a rear surface (one surface) 11 b abutting on the pump chamber P, and a front surface (the other surface) 11 c on which the laminated piezoelectric element 12 is formed. A concave portion 22 a corresponding to the wiring protrusion 11 a may be formed in the middle housing 22 so as to face the pump chamber P.

The laminated piezoelectric element 12 may have a two-layer structure of a lower piezoelectric element layer 12 a and an upper piezoelectric element layer 12 b formed on the front surface 11 c of the main shim 11 in this order, and may face the air chamber A. An intermediate electrode layer 13 a may be interposed between the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b. The intermediate electrode layer 13 a may serve as a neutral layer that electrically insulates the lower piezoelectric element layer 12 a from the upper piezoelectric element layer 12 b. The lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may have the same shape and thickness, and the diameter of each of the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may be equal to or slightly smaller than that of a circular portion of the main shim 11.

The lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may be polarized in opposite directions, as represented by triangles depicted in FIG. 4. When positive and negative voltages are applied, the piezoelectric element (layer) may be elastically deformed in the direction in which the surface area thereof increases or decreases. The lower piezoelectric element layer 12 a close to the main shim 11 may be electrically connected to a second feeder line 15 through a shim-side electrode layer 13 b and the main shim 11, and the upper piezoelectric element layer 12 b close to the air chamber A may be electrically connected to a first feeder line 14 through a surface electrode layer 13 c and the ring-shaped electrode terminal 29. In other words, the lower piezoelectric S element layer 12 a and the upper piezoelectric element layer 12 b may be electrically connected in series to each other (series connection).

The series type laminated piezoelectric element 12 may be formed as follows: the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may be individually formed; a polarizing process may be performed on the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b to polarize them in opposite directions; and the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may be electrically connected in series to each other. Specifically, the lower piezoelectric element layer 12 a may be formed as follows: a piezoelectric green sheet may be cut into a circular shape in plan view by dies cutting; a single-layer sheet or a laminate of a plurality of sheets may be baked; electrode layers (the shim-side electrode layer 13 b and the intermediate electrode layer 13 a) may be formed on the front and rear surfaces of the baked circular sheet; and a polarizing process may be performed on the circular sheet using the electrode layers formed on the front and rear surfaces thereof. The upper piezoelectric element layer 12 b may be formed as follows: a piezoelectric green sheet may be cut into a circular shape in plan view by dies cutting; a single-layer sheet or a laminate of a plurality of sheets may be baked; electrode layers (the surface electrode layer 13 c and the intermediate electrode layer la) may be formed on the front and rear surfaces of the baked circular sheet; and a polarizing process may be performed on the circular sheet using the electrode layers formed on the front and rear surfaces thereof to polarize the circular sheet in a direction opposite to the polarization direction of the lower piezoelectric element layer 12 a. Then, the shim-side electrode layer 13 b of the lower piezoelectric element layer 12 a may be adhered to the shim 11, and the intermediate electrode layers 13 a of the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may be adhered to each other. In this case, for example, a conductive resin adhesive may be used to bond the layers. In this way, the laminated piezoelectric element 12 including the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b that are polarized in opposite directions and electrically connected in series to each other may be obtained. Accordingly, a side electrode or a through hole electrode for a polarizing process may not be needed. Therefore, the series type laminated piezoelectric element 12 may be easily formed. The overall thickness of the laminated piezoelectric element 12 may be in a range of about 50 to about 1000 μm. In addition, a baking process and a polarizing process may be sequentially performed to form the series type laminated piezoelectric element 12.

In the laminated piezoelectric element 12, the surface electrode layer 13 c exposed to the air chamber A may be formed of Au. Meanwhile, the intermediate electrode layer 13 a and the shim-side electrode layer 13 b may be formed of Au, Ag, or an Ag-based conductive material including Ag. Since Au is a conductive material having migration resistance, Au may prevent the migration of the surface electrode layer 13 c due to driving for a long time. Meanwhile, since the intermediate electrode layer 13 a and the shim-side electrode layer 13 b that are not exposed to the air chamber A do not need migration resistance as much as the surface electrode layer 13 c, they may be formed of Ag or an Ag-based conductive material having good adhesion to the main shim 11. Therefore, the electrode from peeling off due to driving for a long time may be prevented, and manufacturing costs may be reduced, when compared to the structure in which the intermediate electrode layer 13 a and the shim-side electrode layer 13 b are formed of Au. This combination of electrodes may lengthen the life span of the piezoelectric vibrator 10.

The ring-shaped electrode terminal 29 may be a ring-shaped conductive thin metal plate that may be stably connected to the surface electrode layer 13 c without hindering the displacement of the upper piezoelectric element layer 12 b, and may include a ring-shaped portion 29 b adhered to a circumferential portion of the surface S electrode layer 13 c and a wiring protrusion 29 a for electrical connection that extends from the ring-shaped portion 29 b. The wiring protrusion 29 a may be electrically connected to the first feeder line 14. The wiring protrusion 29 a and the wiring protrusion 11 a of the main shim 11 may form a pair, and may be accommodated in the concave portion 22 a of the middle housing 22. The ring-shaped electrode terminal 29 may be formed of, for example, 42 alloy with a thickness of about 30 μm.

As shown in FIGS. 3 and 4, in the piezoelectric vibrator 10, both sides of a circumferential portion of the laminated piezoelectric element 12 may be supported by a pair of ring-shaped elastic support members (the O-ring 27 and the guide 28). The O-ring 27 may be provided between the middle housing 22 and the piezoelectric vibrator 10, and may come into contact with a circumferential portion of the rear surface 11 b of the main shim 11, and may apply pressure upward in FIGS. 3 and 4. Meanwhile, the guide 28 may provided between the upper housing 23 and the piezoelectric vibrator 10, may come into contact with the ring-shaped electrode terminal 29 that is adhered to the surface electrode layer 13 c of the laminated piezoelectric element 12, and may press a circumferential portion of the laminated piezoelectric element 12 through the ring-shaped electrode terminal 29 in the downward direction of the drawings. When both sides of the laminated piezoelectric element 12 are supported in this way, the mechanical strength (support strength) of the piezoelectric vibrator 10 may be increased, and the closing pressure thereof (the internal pressure of a discharge passage (system) when a suction umbrella and a discharge umbrella may be closed (when no liquid flows)). In addition, since a pair of ring-shaped support members 27 and 28 come into contact with a circumferential portion of the laminated piezoelectric element 12 that is minimally deformed, the ring-shaped support members may not substantially hinder the displacement of the laminated piezoelectric element 12. Further, the first feeder line 14 may be connected to the surface electrode layer 13 c by, for example, soldering, instead of the ring-shaped electrode terminal 29, and the surface electrode layer 13 c of the laminated piezoelectric element 12 may be directly supported by the ring-shaped support member 28.

In the piezoelectric pump 20 having the above-mentioned support structure, when an alternating electric field is applied between the first feeder line 14 and the second feeder line 15, at the moment when a positive voltage is applied to the first feeder line 14 and a negative voltage is applied to the second feeder line 15, as represented by arrows in FIG. 4, the surface area of the lower piezoelectric element layer 12 a may increase, and the surface area of the upper piezoelectric element layer 12 b may decrease. Then, the laminated piezoelectric element 12 may deform the piezoelectric vibrator 10 to protrude downward in FIG. 4 (generates a couple of forces F). In this state, when the levels of the voltages applied to the first feeder line 14 and the second feeder line 15 are reversed, the laminated piezoelectric element 12 may deform the piezoelectric vibrator 10 to protrude upward in FIG. 4. When this operation is repeated, the piezoelectric vibrator 10 may be vibrated. In this case, the amplitude of the vibration may be larger than that in the structure in which the laminated piezoelectric element 12 includes a single piezoelectric element layer. During a pumping operation, pressure may be applied to the passage due to liquid flowing through the passage. As described above, in this embodiment, a pair of ring-shaped support members 27 and 28 support both sides of a circumferential portion of the laminated piezoelectric element 12, that is, closing pressure may be kept at a high level. Therefore, a stable pumping operation even when pressure is applied to the passage due to the liquid flowing through the passage may be performed.

FIGS. 5 and 6 depict a piezoelectric vibrator 210 and a support structure thereof, according to an embodiment of the present disclosure. In this example, which is a variation of the embodiment of FIG. 3, instead of the series type laminated piezoelectric element 12 and the ring-shaped electrode terminal 29, a parallel type laminated piezoelectric element 212, a ring-shaped electrode terminal 29, and a rod-shaped electrode terminal 29′ may be provided.

The laminated piezoelectric element 212 may have a two-layer structure of the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b formed on the front surface 11 c of the main shim 11 in this order, and may face the air chamber A. The intermediate electrode layer 13 a may be interposed between the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b. The intermediate electrode layer 13 a may serve as a neutral layer that electrically insulates the lower piezoelectric element layer 12 a from the upper piezoelectric element layer 12 b. The lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may have the same shape and thickness, and the diameter of each of the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may be equal to or slightly smaller than that of a circular portion of the main shim 11.

The lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may be polarized in the same direction, as represented by triangles depicted in FIG. 6. The lower piezoelectric element layer 12 a may be electrically connected to the main shim 11 through the shim-side electrode layer 13 b. The main shim 11 and the surface electrode layer 13 c formed on one surface of the upper piezoelectric element layer 12 b facing the air chamber A may be electrically connected to the first feeder line 14. The first feeder line 14 may be connected to the wiring protrusion 11 a of the main shim 11 and the wiring protrusion 29 a of the ring-shaped electrode terminal 29, and the ring-shaped electrode terminal 29 may be adhered to the surface electrode layer 13 c. The intermediate electrode layer 13 a may be electrically connected to the second feeder line 15 through a side electrode 13 d formed on the side of the upper piezoelectric element layer 12 b, a lead electrode 13 e formed on the surface of the upper piezoelectric element layer 12 b, and the rod-shaped electrode terminal 29′ adhered to the lead electrode 13 e. In other words, the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may be electrically connected in parallel to each other (parallel connection) The intermediate electrode layer la and the lead electrode 13 e may be electrically connected to each other by a through hole electrode, instead of the side electrode 13 d. In the the embodiment of FIG. 5, instead of using the ring-shaped electrode terminal 29 and the rod-shaped electrode terminal 29′, the first feeder line 14 may be soldered to the surface electrode layer 13 c, the second feeder line 15 may be soldered to the lead electrode 13 e, and the surface electrode layer 13 c of the laminated piezoelectric element 212 may be directly supported by the ring-shaped support member 28.

In this embodiment, the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may be polarized in the same direction. Therefore, when an alternating electric field is applied between the first feeder line 14 and the second feeder line 15, the surface area of one of the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may increase, but the surface area of the other piezoelectric element layer may decrease. The amplitude of the vibration of the piezoelectric vibrator 210 may be larger than that in the structure in which a piezoelectric element of the piezoelectric vibrator 210 includes only a single piezoelectric element layer. In this case, a circumferential portion of the rear surface 11 b of the main shim 11 may be pressed upward in the drawings by the O-ring 27, and a circumferential portion of the laminated piezoelectric element 212 may be pressed downward in the drawings by the guide 28 through the ring-shaped electrode terminal 29 and the rod-shaped electrode terminal 29′. Therefore, the piezoelectric vibrator 210 may be fluid-tightly sealed and supported between the middle housing 22 and the upper housing 23. As a result, similar to the embodiment of FIG. 3, the mechanical strength and closing pressure of the piezoelectric vibrator 210 may be improved.

FIG. 7 depicts a piezoelectric vibrator 310 and a support structure thereof, according to an embodiment of the present disclosure. In this embodiment, which is a variation of the embodiment of FIG. 3, in addition to the main shim 11, an intermediate shim 40 may be interposed between the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b. The intermediate shim 40 may be a circular or ring-shaped elastic metal member (in this embodiment, a circular shape) that may have mechanical recovery and may be deformable with the displacement of the laminated piezoelectric element 312. The mechanical recovery of the intermediate shim 40 may be higher than that of the main shim 11, and the intermediate shim 40 may not substantially hinder the displacement of the laminated piezoelectric element 312. The intermediate shim 40 may be formed of the same material as that forming the main shim 11 to be thicker than the main shim 11. Specifically, the intermediate shim 40 may be formed of, for example, a thin metal plate with a thickness of about 50 to about 600 μm that is made of, for example, 42 alloy. The intermediate shim 40 may improve the mechanical strength of the laminated piezoelectric element 312 and thus the piezoelectric vibrator 310 and may improve the closing pressure of the piezoelectric pump. The intermediate shim 40 may be provided between the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b, that is, in the middle of the laminated piezoelectric element 312. Since the intermediate shim 40 is a neutral sheet for a couple of forces F generated when an alternating electric field is applied to the laminated piezoelectric element 312, the intermediate shim 40 may increase the displacement of the laminated piezoelectric element 312. Intermediate electrode layers 13 a may be provided among the intermediate shim 40, the lower piezoelectric element layer 12 a, and the upper piezoelectric element layer 12 b. In this embodiment, the first feeder line 14 may be connected to the surface electrode layer 13 c by, for example, soldering, instead of the ring-shaped electrode terminal 29, and the ring-shaped support member 28 may directly support the surface electrode layer 13 c of the laminated piezoelectric element 312.

FIG. 8 depicts a piezoelectric vibrator 410 and a support structure thereof, according to an embodiment of the present disclosure. In this embodiment, which is a variation of the embodiment of FIG. 5, in addition to the main shim 11, an intermediate shim 40 may be interposed between the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b. The intermediate shim 40 may be a circular or ring-shaped elastic metal member (in this embodiment, a circular shape) that may have mechanical recovery and may be deformable with the displacement of a laminated piezoelectric element 412. The mechanical recovery of the intermediate shim 40 may be higher than that of the main shim 11, and the intermediate shim 40 may not substantially hinder the displacement of the laminated piezoelectric element 412. The intermediate shim 40 may be formed of the same material as that forming the main shim 11 and may be thicker than the main shim 11. Specifically, the intermediate shim 40 may be formed of, for example, a thin metal plate with a thickness of about 50 to about 600 μm that is made of, for example, 42 alloy. The intermediate shim 40 may improve the mechanical strength of the laminated piezoelectric element 412 and thus the piezoelectric vibrator 410 and may improve closing pressure of the piezoelectric pump. The intermediate shim 40 may be provided between the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b, that is, in the middle of the laminated piezoelectric element 412. Since the intermediate shim 40 is a neutral sheet for a couple of forces F generated when an alternating electric field is applied to the laminated piezoelectric element 412, the intermediate shim 40 may increase the displacement of the laminated piezoelectric element 412. Intermediate electrode layers la may be provided among the intermediate shim 40, the lower piezoelectric element layer 12 a, and the upper piezoelectric element layer 12 b. Since the intermediate shim 40 also serves as an electrode terminal for electrically connecting the intermediate electrode layers 13 a and the second feeder line 15, the side electrode 13 d, the lead electrode 13 e, and the rod-shaped electrode terminal 29′ of the second embodiment may not be needed, which makes it possible to easily connect wiring lines. The shim-side electrode layer 13 b and the surface electrode layer 13 c may be electrically connected to the first feeder line 14 through the main shim 11 and the ring-shaped electrode terminal 29. In the fourth embodiment, the first feeder line 14 may be connected to the surface electrode layer 13 c by, for example, soldering, instead of the ring-shaped electrode terminal 29, and the ring-shaped support member 28 may directly support the surface electrode layer 13 c of the laminated piezoelectric element 412.

FIG. 9 depicts a piezoelectric vibrator 510 and a support structure thereof, according to an embodiment of the present disclosure. In this embodiment, which is a variation of the embodiment of FIG. 7, the upper piezoelectric element layer 12 b may have a smaller diameter than the lower piezoelectric element layer 12 a, and a pair of ring-shaped support members (the O-ring 27 and the guide 28) may support both sides of a circumferential portion of the lower piezoelectric element layer 12 a. The overall shape of a laminated piezoelectric element 512 may be a convex shape in a cross-sectional view, and the intermediate electrode layers 13 a and the intermediate shim 40 may each have a diameter that is equal to that of the upper piezoelectric element layer 12 b. The intermediate electrode layer 13 a formed on the lower piezoelectric element layer 12 a may have a diameter that is equal to that of the lower piezoelectric element layer 12 a. A circumferential portion of the lower piezoelectric element layer 12 a may be exposed from the upper piezoelectric element layer 12 b, and the exposed portion may come into direct contact with the guide 28. The guide 28 may be formed in a ring shape having a diameter equal to that of the lower piezoelectric element layer 12 a, but may not contact the upper piezoelectric element layer 12 b. In other words, the upper piezoelectric element layer 12 b may be deformable without being restricted by the guide 28. According to this embodiment, since the support members support both sides of a circumferential portion of the lower piezoelectric element layer 12 a, the upper piezoelectric element layer 12 b while improving the mechanical strength of the piezoelectric vibrator 510 and improving closing pressure of the piezoelectric pump may be deformed, thereby increasing the displacement of the piezoelectric vibrator 510. In addition, since the guide 28 is provided in a step portion between the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b, the thickness of a housing may be reduced. In this embodiment, the intermediate shim 40 may be interposed between the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b. However, the intermediate shim 40 may not be provided. Further, instead of the series type laminated piezoelectric element 512, a parallel type laminated piezoelectric element may be used. In this example, the first feeder line 14 may be connected to the surface electrode layer 13 c by, for example, soldering, instead of the ring-shaped electrode terminal 29.

FIG. 10 depicts a piezoelectric vibrator 610 and a support structure thereof, according to an embodiment of the present disclosure. In this embodiment, which is a variation of the embodiment of FIG. 9, the intermediate shim 40 may extend up to a circumferential portion of the lower piezoelectric element layer 12 a, and the guide 28 may support a circumferential portion of the lower piezoelectric element layer 12 a with the intermediate shim 40 interposed therebetween. The diameters of the intermediate shim 40 and the lower piezoelectric element layer 12 a may be equal to each other. The intermediate shim 40 interposed between the guide 28 and the lower piezoelectric element layer 12 a may improve the strength of the support portion, may improve the mechanical strength of the piezoelectric vibrator 610, and may improve closing pressure of the piezoelectric pump. In this embodiment, a series type laminated piezoelectric element 612 may be used, but a parallel type laminated piezoelectric element may also be used. In this example, the first feeder line 14 may be connected to the surface electrode layer 13 c by, for example, soldering, instead of the ring-shaped electrode terminal 29.

FIG. 11 depicts a graph illustrating a flow rate [ml/min] and pressure [kPa] measured at a predetermined position in a flow passage in Example 1 in which a pair of ring-shaped support members 27 and 28 support both sides of a circumferential portion of the laminated piezoelectric element 12 of the piezoelectric vibrator 310 and in Comparative example 1 (FIG. 13) in which a pair of ring-shaped support members 27 and 28 support both sides of a circumferential portion of the main shim 11 of the piezoelectric vibrator 310. The measurement may be performed while operating the piezoelectric vibrator 310 at driving frequencies of 30 Hz and 60 Hz. In the graph shown in FIG. 11, circles indicate measured values when the piezoelectric vibrator 310 may be operated at a driving frequency of 30 Hz, and rectangles indicate measured values when the piezoelectric vibrator 310 may be operated at a driving frequency of 60 Hz.

The piezoelectric vibrator 310 according to the embodiment shown in FIG. 7 may be used, and the intermediate shim 40 may be interposed between the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b. Example 1 differs from Comparative example 1 in the support positions of a pair of ring-shaped support members 27 and 28. In Example 1, the main shim 11 may have a thickness of 0.03 mm, the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may have a thickness of 0.2 mm, and the intermediate shim 40 may have a thickness of 0.1 mm. In Comparative example 1, the main shim 11 may have a thickness of 0.03 mm, the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may have a thickness of 0.3 mm, and the intermediate shim 40 may have a thickness of 0.05 mm. In Example 1, the measurement may be made under more severe conditions than those in Comparative example 1 in order to clarify the effects of Example 1. In Comparative example 1, the thickness of the intermediate shim 40 may be smaller than that in Example 1 by 0.05 mm, but the mechanical strength of Comparative example 1 and Example 1 may be dominated by the thicknesses of the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b. Therefore, in the measurement, the influence of the difference in the thickness of the intermediate shim 40 on the mechanical strength may be negligible.

As depicted in FIG. 11, even when the piezoelectric vibrator 310 is operated at a driving frequency of 30 Hz or 60 Hz, Example 1 in which both sides of a circumferential portion of the laminated piezoelectric element 12 are supported by the support members may have higher closing pressure (pressure when no liquid flows) than Comparative example 1. When the driving frequency of the piezoelectric vibrator 310 is changed from 30 Hz to 60 Hz, there may be no change in closing pressure in Comparative example 1. In Example 1, there may be no reduction in closing pressure, and thus high-speed driving may not be affected. In addition, in Example 1, the flow rate of liquid (the displacement of the piezoelectric vibrator 310) may be slightly lower than that in Comparative example 1. Even when the piezoelectric vibrator 310 is operated at a driving frequency of 60 Hz, the flow rate may be kept at 50 ml/min or less, which is not considerably lower than that in Comparative example 1.

FIG. 12 depicts a graph illustrating a flow rate [ml/min] and pressure [kPa] measured at a predetermined position in a flow passage in Example 1 in which a pair of ring-shaped support members 27 and 28 support both sides of a circumferential portion of the laminated piezoelectric element 12 of the piezoelectric vibrator 510 and in Comparative example 1 (FIG. 13). The measurement may be performed while operating the piezoelectric vibrators 310 and 510 at driving frequencies of 30 Hz and 60 Hz. In the graph shown in FIG. 14, circles indicate measured values when the piezoelectric vibrators 310 and 510 may be operated at a driving frequency of 30 Hz, and rectangles indicate measured values when the piezoelectric vibrators 310 and 510 may be operated at a driving frequency of 60 Hz.

The piezoelectric vibrator 510 according to the embodiment shown in FIG. 9 may be used. The upper piezoelectric element layer 12 b may have a smaller diameter than the lower piezoelectric element layer 12 a, and the guide 28 may support a circumferential portion of the lower piezoelectric element layer 12 a that extends up to the upper piezoelectric element layer 12 b. The intermediate shim 40 may be interposed between the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b. Comparative example 1 may be similar to Example 2 except for the size of the upper piezoelectric element layer 12 b and the support positions of a pair of ring-shaped support members 27 and 28. Specifically, the main shim 11 may have a thickness of 0.03 mm, the lower piezoelectric element layer 12 a and the upper piezoelectric element layer 12 b may each have a thickness of 0.2 mm, and the intermediate shim 40 may have a thickness of 0.05 mm.

As depicted in FIG. 12, even when the piezoelectric vibrators 310 and 510 are operated at a driving frequency of 30 Hz or 60 Hz, Example 2 in which both sides of a circumferential portion of the laminated piezoelectric element 512 are supported by the support members may have higher closing pressure (pressure when no liquid flows) than Comparative example 1. When the driving frequency of the piezoelectric vibrators 310 and 510 is changed from 30 Hz to 60 Hz, there may be no change in closing pressure in Comparative example 1. In Example 2, there may be no reduction in closing pressure, and thus high-speed driving may not be affected. In addition, in Example 2, the flow rate of liquid (the displacement of the piezoelectric vibrator) may be slightly lower than that in Comparative example 1. Even when the piezoelectric vibrator is operated at a driving frequency of 60 Hz, the flow rate may be kept at 60 ml/min or less, which is not considerably lower than that in Comparative example 1.

As described above, according to this embodiment, a pair of ring-shaped support members 27 and 28 support both sides of a circumferential portion of the laminated piezoelectric element 12 (212, 312, 412, 512, and 612). Therefore, the mechanical strength and closing pressure of the piezoelectric vibrator 10 (210, 310, 410, 510, and 610) may be increased without substantially hindering the displacement of the piezoelectric vibrator 10 (210, 310, 410, 510, and 610). As a result, the piezoelectric vibrator 10 (210, 310, 410, 510, and 610) may be prevented from being deformed due to the internal pressure of a flow passage, and thus may stably perform a pumping operation. In this way, a reduction in the thickness of the main shim 11 may be more easily handled.

In the above-described embodiments, in the piezoelectric vibrator 10 (210, 310, 410, 510, and 610), the laminated piezoelectric element may be formed on one of the front and rear surfaces of the main shim 11, but the present disclosure is not limited thereto. The present disclosure may be applied to a piezoelectric vibrator having piezoelectric elements, each including at least one piezoelectric element layer, formed on both the front and rear surfaces of a main shim. In the piezoelectric vibrator having the piezoelectric elements, each including at least one piezoelectric element layer, formed on both the front and rear surfaces of the main shim, both sides of a circumferential portion of the piezoelectric element may be supported by the O-ring 27 and the guide 28. The guide 28 may support the entire circumference of the piezoelectric element or a portion of the circumference of the piezoelectric element. The piezoelectric element of the piezoelectric vibrator may include a single layer or three or more layers. 

1. A piezoelectric pump comprising: a piezoelectric vibrator including a main shim that is formed of a conductive thin metal plate and a piezoelectric element layer that is formed on the main shim; and a pair of ring-shaped support members that support front and rear sides of a circumferential portion of the piezoelectric vibrator such that a pump chamber and an air chamber formed on the front and rear sides of the piezoelectric vibrator are fluid-tightly sealed, wherein the ring-shaped support members support both sides of a circumferential portion of the piezoelectric element layer of the piezoelectric vibrator, and the piezoelectric vibrator is vibrated to perform a pumping operation.
 2. The piezoelectric pump of claim 1, wherein: in the piezoelectric vibrator, one surface of the main shim abuts on the pump chamber, and at least one piezoelectric element layer is formed on the other surface of the main shim, and one of the pair of ring-shaped support members close to the pump chamber comes into contact with a circumferential portion of the main shim, and the other ring-shaped support member close to the air chamber comes into contact with the circumferential portion of the piezoelectric element layer.
 3. The piezoelectric pump of claim 2, wherein the piezoelectric element layer of the piezoelectric vibrator comprises: a lower piezoelectric element layer that is formed on the other surface of the main shim; and an upper piezoelectric element layer that is formed on the lower piezoelectric element layer so as to be electrically insulated from the lower piezoelectric element layer, wherein the upper piezoelectric element layer has a smaller diameter than the lower piezoelectric element layer, and wherein the ring-shaped support member close to the air chamber is provided such that a circumferential portion of the upper piezoelectric element layer is opened and both sides of a circumferential portion of the lower piezoelectric element layer are supported.
 4. The piezoelectric pump of claim 2, wherein: an intermediate shim formed of an elastic metal material having mechanical recovery is provided between a plurality of piezoelectric element layers of the piezoelectric vibrator.
 5. The piezoelectric pump claim 4, wherein the intermediate shim has higher mechanical recovery than the main shim.
 6. The piezoelectric pump of claim 4, wherein: the intermediate shim has a larger diameter than the piezoelectric element layer formed on the intermediate shim, and the pair of ring-shaped support members support both sides of a circumferential portion of a laminate of the intermediate shim, the main shim, and the piezoelectric element layer interposed between the two shims. 